The object of the proposed research is to continue investigations on the reactions of singlet oxygen with organic substrates, particularly heterocyclic and aromatic systems, which may be incorporated in molecules of biological interest. Studies on indoles, imidazoles, pyrroles, and other oxygen-sensitive constituents of amino acids involved in the photodynamic effect will be emphasized as outlined earlier. Particular attention will be given to the photooxygenation of enamines in view of significant new results obtained in this phase of the work during the past year. We have found that oxygenation of enamines may be controlled so as to yield dioxetanes which undergo a second-stage Deta-elimination reaction without carbon-carbon bond cleavage. These findings are of special interest in connection with potentially useful synthetic application of enamine-singlet oxygen reactions. Moreover, they are of significance in understanding the mechanism of oxygenation of a wide variety of electronrich olefinic systems which are present as enamines or as enamine units in biologically important heterocyclic molecules (containing pyrroles, imidazoles, indoles and purines) which are reactive singlet oxygen acceptors.